In recent years, wireless communication devices in compliance with wireless LAN standards that are stipulated in IEEE 802.11 have drastically come into use, and many wireless communication devices that use an unlicensed band of 2.4 GHz or 5 GHz have been deployed. In the unlicensed band, a state of a channel that is scheduled for transmission is determined with prior carrier sense, and the transmission is started if a state where the transmission is available is reached. For this reason, in an environment where many wireless communication devices are mixedly present in the unlicensed band, a plurality of neighboring wireless communication devices are in suspending transmission while a certain wireless communication device performs transmission, and thus throughput is decreased.
Incidentally, in IEEE 802.11ax, the introduction of a technology that controls the interference detection threshold which is used in order to determine the state of the channel with the carrier sense is expected with (Non-Patent Document 1). With the technology, control is performed in such a manner that the interference detection threshold becomes higher than in the related art. Thus, although an interference power level from a neighboring wireless communication cell is observed, there are many opportunities to determine that a channel is transmittable. It is noted that in the case of a wireless LAN, the interference detection threshold is equivalent to a carrier sense threshold.
Furthermore, in Non-Patent Document 1, a technology is disclosed that controls the interference detection threshold and, along with this, controls a transmission power level. Moreover, a procedure is also expected in which an upper limit is imposed on the interference detection threshold and the transmission power level and in which, along with this, control is performed in conjunction with each of the values.
With these controls, it is expected that, in an environment in which the number of transmission opportunities for wireless communication devices is reduced due to interference with each other, more transmission opportunities are acquired than before and thus the throughput is improved. Moreover, because the same procedure is applied even if an LTE signal is transmitted in the unlicensed band, it is thought that the control of the interference detection threshold and the transmission power level has a close relationship with communication quality of the unlicensed band.
Moreover, in Non-Patent Document 2, a technology is disclosed that suppresses the interference with each other on the same channel using pieces of information of interference signal that are collected from a plurality of wireless communication devices, and control is possible that improves frequency utilization efficiency of an entire wireless communication system, not utilization efficiency of an individual wireless communication device.
Non-Patent Document 1: IEEE P802.11 ax™ Draft 0.1, March 2016
Non-Patent Document 2: Koji Yamamoto and Hirantha Abeysekera, “Analysis of Inversely Proportional Setting of Transmission Power and Carrier Sense Threshold in WLANs”, IEICE Technical Report, June 2016